Most conventional gear burnishing machines include toothed rotary tools supported in a spaced relationship to each other to receive a toothed gear that is rotatably supported on a work spindle about an axis parallel to the axes about which the tools rotate. Driving of one or more of the tools meshes the tool teeth with the gear teeth so that pressure applied therebetween causes the harder teeth of the tools to remove surface defects from the softer gear teeth. Removal of the surface defects on the burnished gears lengthens their useful life and also mitigates gear noise during use.
In order to have high production capacity, burnishing machines must include suitable mechanisms for loading and unloading the gears. The work spindles that rotatably support the gears during the burnishing are conventionally supported for movement so as to perform the loading and unloading of the gears. Automatic conveyors have also been utilized to feed gear burnishing machines and receive burnished gears therefrom after being processed by the machines.
The United States Patent of Anderson No. 4,080,699, which is assigned to the assignee of the present invention and the entire disclosure of which is hereby incorporated by reference, discloses apparatus and a method for burnishing gears incorporating a pair of spaced gear racks having opposed forming faces for meshing with a toothed gear to be burnished during driven rack movement so that the meshing of the rack and gear teeth provides the sole support for the gear as the rack teeth concomitantly burnish the gear teeth. Very good results are achieved in performing the burnishing operation by virtue of the manner in which the rack teeth mesh with the gear teeth to provide the burnishing thereof and the rotational support for the gear being burnished. It is believed that the superior results are achieved due to the freedom of the axis of gear rotation to move with respect to the racks as the rack teeth engage defects on the gear teeth.
When gear teeth are burnished by either a rotary or rack burnishing operation like those described above, the natural flow of the metal gear teeth provides the opposite faces of each tooth with a slight crown intermediate the axial ends of the gear. Thus, at any selected radial position from the axis of gear rotation through the tooth, a straight line between the opposite axial ends of either tooth face will be located inwardly from the axial intermediate portion of that face by a certain distance which is normally on the order of one to four ten-thousandths of an inch. Such axial crowns on gear tooth faces provide meshing engagement of the gear teeth at the axial intermediate portions of the teeth where the greatest strength resides and thus enhance gear performance and durability.